day = 3

def get_sunday():
    return 'Sunday'

def get_monday():
    return 'Monday'

def get_tuesday():
    return 'Tuesday'

def get_default():
    return 'Unkown'

switcher = {
    0 : get_sunday,
    1 : get_monday,
    2 : get_tuesday
}

# get的第二个参数代表day找不到时返回的字符串
day_name = switcher.get(day,get_default)()
print(day_name)